Playrate isn't everything...
Some champions are just popular, Thresh is just cool and has a lot of potential. Him being played a lot doesn't mean he is 'busted'. It means people want to play him. Playrate is a terrible measure of balance, because Ahri will always have more people wanting to play her than Aurelion even when he was busted, just because she is fun to play, has a fluid and smooth kit, and yes... a lot of people find her attractive. And yet he was just recently broken and was nerfed at the end of S6, because he was too strong, despite his low play rate.
People want to play things that: Fulfill a fantasy they like. Are nice too look at/hear. Feel good to play. Challenge them/fit their personality. Their favorite streamer plays them. It has high growth potential/is simple to use.
Yes, some people ARE just looking for the currently OP champions, FotM players. So play rates matter... a little. But seeing "x champion is played in x amount of games!" doesn't mean they are broken. It might just mean people like them.
Some champions are picked only because they are considered OP - (I took a break for some months and when I came back to Lol everyone was playing
- a champion with a pretty damn boring kit just because of her broken crits and traps)
Guys like
are slow, ugly and played only when overpowered.
is neither good to look at or hear